1. Field of the Invention
The present invention relates to crimping equipment used in the manufacturing of fibers, especially polyolefin fibers, and a process for crimping fibers. Further, this invention relates to fibers for nonwoven applications, especially polyolefin fibers such as polypropylene fibers.
2. Discussion of the Background Information
Crimpers are used in processing fibers to add bulkiness, cohesiveness, and cardability. A crimper works by having two driven rolls pinch the tow and force it into a confined space, known as a stuffer box. The stuffer box includes two doctor blades positioned close to the driven rollers, and side plates. Crimping occurs because the filaments are forced against a cake of more slowly moving filaments. Traditionally heat, in the form of steam, has been used ahead of the crimper to soften the filaments prior to crimping. Additionally, heat, also in the form of steam, is fed through holes in the doctor blades into the stuffer box to lubricate the tow. As disclosed by McGill, Modern Crimping Techniques, Fiber World, pp. 51-55, the entire disclosure of which is hereby incorporated by reference, the doctor blades can be positioned at a variety of angles in relationship to the driven rolls. Further, McGill discloses that the top doctor blade may be hinged, and that the driven rolls may be hollow in order to circulate temperature-control fluids.
U.S. Pat. No. 4,620,345, to Fleissner, the entire disclosure of which is hereby incorporated by reference, discloses an apparatus for crimping including a pair of delivery rolls, a stuffer box, a chute following an outlet of the stuffer box for supplying the crimped fiber to a sieve drum for setting the crimp, with the sieve drum being traversed by cooling air.
Technological changes in fibers, involving lower denier per filament, lower draw ratios, and skin/core structure have made crimping more difficult and has lowered usable temperature levels in the crimper. Specifically, the application of too much heat to the fibers causes them to fuse. By lowering the temperature, the undesirable sticking together of filaments can be avoided; however, the use of lower temperatures makes it difficult to reach desired crimp levels.